Optical disk systems can be used to perform various biological, chemical or bio-chemical assays, such as genetic-based assays or immunoassays. In such systems, a rotatable disk with multiple chambers can be used as a medium for storing and processing fluid specimens, such as blood, plasma, serum, urine or other fluid. The multiple chambers on one disk can allow for simultaneous processing of multiple portions of one sample, or of multiple samples, thereby reducing the time and cost to process multiple samples, or portions of one sample.